Recently, the information recording density in magnetic recording systems such as a Video Tape Recorder (VTR) and a Hard Disk Drive (HDD), and the like has greatly increased.
In these high density magnetic recordings information or data is recorded into a recording material by using a shortwave frequency recording, so it is required for the recording media to have a large coercive force. In addition, it is also required for a recording head to use a soft magnetic material having a high saturation magnetic flux density and it is also required for the recording head to have a good frequency property corresponding to the increase in recording frequency. In particular, it is required that the magnetic head be applied to a HD-VTR (High Definition Video Tape Recorder) and a high density HDD head operate for frequencies of up to several ten MHz.
On the other hand, in miniaturization of various electronic devices, it is also required to miniaturize power source section in the electronic devices. In order to answer the above requirements, a switching power supply in which switching frequency is increased is used in electronic devices. Although the switching power supply has been miniaturized by using miniaturized magnetic components such as a high frequency inductor or a high frequency transformer, however it is difficult to miniaturize the magnetic components.
In order to overcome the problem described above, a thin film magnetic element using a soft magnetic thin film is currently under investigation. Since this thin film magnetic element can operate for frequencies of a few MHz to several ten Mhz, it would be used for the switching power supply.
In addition, the soft magnetic material is used for the high frequency magnetic elements described above, soft magnetic materials of alloy system, oxide system, nitrite system, and the like have been developed.
As shown in FIG. 1, a high frequency core loss measuring device which operates in a range up to 20 Mhz has been developed as a magnetic property measuring means for a bulk magnetic material. This high frequency core loss measuring system is actually used as an evaluation equipment for research of material development. A feature of the measuring method for measuring the property of the bulk magnetic material is that the intrinsic property of material can be measured without demagnetization effect by using a ring-shaped soft magnetic material sample T.
However, there are many problems when the measuring method of the conventional magnetic property measuring system shown in FIG. 1 is directly utilized for a thin film sample. In FIG. 1, the sine wave signal generator 101 provides a frequency signal. The power amplifier 103 provides current to the sample T via lines 105a, b. A wave-form storage device 109 stores the waveform provided through signal transfer lines 107a, b. A computer 111 controls the sine wave signal generator 101, the power amplifier 103 and the wave-form storage device 109. For example, in one of the problems, although a measuring frequency is usually limited by a self-resonance frequency, it is difficult to increase a self-resonance frequency because a coil is directly wound in a soft magnetic thin film as a sample in the measuring method shown in FIG. 1. Further, a thin film is usually formed on a substrate and the thin film to be measured must be wound together with a coil, so that a large measuring error is caused in results measured for the thin film by the existence of the substrate. In order to eliminate the measuring error, Calcagno et al. have proposed a magnetic thin film measuring method using an 8-figure coil. (see the reference of Rev. Sci. Instrum., Vol. 46, No. 7, pp. 904-908, 1975)
FIGS. 2A and 2B show the principle of the magnetic thin film measuring method. In the magnetic thin film measuring method using the 8-figure coil, first, a thin film 123 as a sample of a soft magnetic material is formed on a substrate 125. Then, the thin film formed is located in a uniform high frequency magnetic field and placed in the upper coil (or the lower coil) of the 8-figure coil 121a in order to measure the properties of the thin film.
The magnetic thin film measuring method will now be described below abstractly. Here, we assume that a sample of a soft magnetic material or a body to be measured is placed in the upper coil just as the thin film penetrates the upper coil. The magnetic flux .phi..sub.o passing through the upper coil is: EQU .phi..sub.0 =S.sub.b .multidot..mu..sub.0 (H-H.sub.d)+S.sub.a .multidot.I(1)
where S.sub.a is a sectional area of a soft magnetic material to be measured, S.sub.b is a sectional area of the upper section of the 8-figure coil 121a shown in FIG. 2B, H is an external high frequency magnetic field, is vacuum magnetic permeability, H.sub.d is a demagnetizing field in the inner section of a sample, and I is a magnetization of a sample of a thin film.
The magnetic flux .phi. passing through the lower coil in which the soft magnetic material sample is not placed is: EQU .phi..sub.0 =S.sub.b .multidot..mu..sub.0 (H-H.sub.r) (2)
where H.sub.r is the demagnetizing field in the entire section of a sample.
A pair of coils of the 8-figure coil are connected to each other in anti-polarity. Therefore the value of an induced voltage becomes following: EQU V.sub.8 =-(d.phi..sub.0 /dt-d.phi./dt) =-S.sub.0 .multidot.(dI/dt)+S.sub.a .multidot.(d(H.sub.d -H.sub.r)/dt) (3),
where H is an external high frequency magnetic field,
Here, when the Hr is approximately equivalent to the H.sub.d, the magnetization I of the sample thin film is given as follows: EQU I=(1/S.sub.a).intg.V.sub.8 .multidot.dt (4).
In addition, in a measuring process, a magnetic field detecting coil 121b is placed adjacent to the sample to detect the external high frequency magnetic field. In this case, the value of H.sub.eff is given as follows: EQU H.sub.eff. =(1/S.sub.c)V.sub.H .multidot.dt (5)
where S.sub.c is a sectional area of a magnetic field detecting coil 121b, shown in FIG. 2B.
Thus, we can know the values of the external magnetic field H and of the magnetization I of the sample of the thin film, when the rate of amplitudes of these values is obtained, the high frequency effective magnetic susceptibility X.sub.Eff. is obtained as follows: EQU X.sub.Eff. =I.sub.m /H.sub.Eff. m (6)
where I.sub.m and H.sub.Eff. m are the peak values.
In addition, the value of the high frequency effective magnetic permeability .mu..sub.Eff. is following: EQU .mu..sub.Eff. =X.sub.Eff. +1 (7).
As described above in detail, the 8-figure measuring method is widely used as a measuring method for a high frequency magnetic permeability because it has good availability. However, the applications of the measuring method are limited only within small signal measurement, for example, magnetic field amplitude of approximately 0.5 A/m.
Further, as shown in FIG. 3, a conductor is only wound in 8-figure form as a 8-figure coil. In this case, the dimension of a looped-area of the upper coil of the 8-figure coil must be equal to that of the lower coil exactly in order to obtain a correct measured value.
However, usually, it is very difficult to form the upper section and the lower section of the 8-figure coil whose looped-areas are equal to each other by using the winding method for winding with a conductor. The dimension error of the looped-areas between the upper section and the lower section of the 8-figure coil effects the measuring accuracy directly.
In order to avoid the conventional problem described above, as shown in FIG. 4, a method for forming a 8-figure coil is proposed by using printed circuit board technology. With the 8-figure coil obtained by the forming method, the dimension accuracy can be easily increased. In an actual measuring process, the dimension error of the 8-figure coil is modified by a calibration based on a detected voltage when a sample to be measured is not inserted in the 8-figure coil.
Further, a sample thin-film is placed in the 8-figure coil as shown in FIG. 2A, in this case, the magnetization change of the entire sample thin-film cannot be detected because a magnetization change of an area positioned only nearby the 8-figure coil is measured. For example, as shown in FIG. 5, when there are triangle magnetic domains in the edge sections of the sample thin-film, the property of a magnetic component with the magnetic thin-film is affected by the existence of the triangle magnetic domains, and the conventional method using the 8-figure coil can detect only a local magnetization change in a sample.
There is the difference between the magnetic property of a sample thin-film itself to be measured and the electrical property of magnetic elements including the triangle magnetic domains generated in the sample thin-film. Specifically, the conventional measuring method cannot detect the magnetization change of the overall property of a soft magnetic material as a sample.
In addition, as shown in FIG. 6, a parallel plane-shaped coil is also often used as a means for generating a high frequency uniform external magnetic field. However, according to the study by the inventors of the present invention, it is apparent that the parallel plane-shaped coil can't generate a homogenous magnetic field. FIGS. 7A to 7C show calculation results about a magnetic field distribution in the parallel plane-shaped coil by using Biot-Savart law.
As shown in FIGS. 7A to 7C, there is a fluctuation of the magnetic field of more than 20 percent in the range of the center point 0.+-.7 mm in the parallel plane-shaped coil.
The fluctuation of the magnetic field, namely irregular magnetic field, affects the measuring accuracy of a sample.
As described above in detail, it is required to perform high frequency magnetic measurements with a large signal operation. For these reasons or requirements, the magnetic property evaluation of these high frequency magnetic elements must be performed in a high frequency magnetic field having a large amplitude which is almost equivalent to an actual amplitude of a high frequency magnetic field in which a soft magnetic material is actually used in application fields.
Moreover, it is required to obtain a method or a technique for evaluating magnetic components affected from the magnetic property of the entire soft magnetic material. However, at present, there is no method for evaluating the effects, so that development of a magnetic recording head, a thin film inductor, a thin film transformer, and the like is limited.